1. Field of the Invention
The present invention relates to systems for feeding and transporting documents and to a system and method for detecting a document trailing edge exiting a feeder.
2. Background Art
A typical system for feeding and transporting documents includes a feeder and a separator in the document feeding portion of the system, and a series of roller pairs or belts in the document transporting portion of the system. In the feeding portion of the system, the feeder acts with the separator to feed documents singly, in order, from a stack. In the transporting portion of the system, the roller pairs and/or belts convey the documents, one at a time, past other processing devices such as readers, printers, and sorters that perform operations on the documents. The feeder is typically a feed wheel, but may take other forms. The separator may be a wheel, but also may take other forms such as a belt. Further, the components in the transporting portion of the system may take a variety of forms. Systems also include a component in the document feeding portion of the system that nudges documents into the nip between the feeder and the separator. A suitable nudger may be a nudger wheel, but may take other forms. An existing document feeder is shown in U.S. Pat. No. 6,199,854. That patent describes a document feeder with a variable speed separator.
In existing systems for transporting documents, operations that depend on the position of the document are generally performed in the transport stage, or transporting portion of the system. For example, U.S. Pat. No. 5,848,784 describes a document separation apparatus. That patent describes the downstream acceleration/deceleration of documents with pinch rollers to adjust document spacing. Although some existing systems may successfully perform operations that depend on the position of the document, these existing systems do have their limitations. In certain situations, it would be desirable to know immediately when a first document trailing edge has left the feeder so that operations can be performed on a second, following, document with the feeder as soon as possible without affecting the first document. Further, it would be desirable to know such information so that operations can be performed on the first, leading, document in the transport stage without the first document being affected by actions of the feeder. Existing systems have a shortcoming in that there is no way to know immediately when a document trailing edge has left the feeder.
For the foregoing reasons, there is a need for a system and method for detecting a document trailing edge exiting a feeder.
It is, therefore, an object of the present invention to provide a system and method for detecting a document trailing edge exiting a feeder.
In carrying out the above object, a system for feeding and transporting documents is provided. Each document has a leading edge and a trailing edge. The system comprises a feeder stage, a transport stage, a tachometer, and control logic. The feeder stage includes a feeder and a separator for receiving a document therebetween and gripping the document with a first grip. The transport stage is downstream of the feeder stage. The transport stage includes an accelerator driver and an accelerator idler for receiving the document therebetween and gripping the document with a second grip that is less than the first grip. When the document is simultaneously gripped by the feeder and separator and gripped by the accelerator driver and accelerator idler, the document slips at the accelerator driver until the document trailing edge exits the feeder and separator. The tachometer is at the accelerator idler. The control logic is configured to detect an acceleration of the tachometer indicating when the document trailing edge exits the feeder and separator, and to provide an output signal.
In a preferred embodiment, the system further comprises a control device receiving the output signal. The control device is configured to perform an operation after the document trailing edge has exited the feeder and separator.
In embodiments of the present invention, the tachometer may include an encoder and generate a pulse sequence. The control logic would then detect the acceleration based on the pulse sequence. Or, the tachometer may generate an analog velocity signal, and the control logic would then detect the acceleration based on the analog velocity signal.
In a preferred embodiment, the system further comprises a feeder tachometer at the feeder. The control logic is configured to detect a relative acceleration of the accelerator idler tachometer with respect to the feeder tachometer indicating when the document trailing edge exits the feeder and separator.
Further, in carrying out the present invention, a method of detecting a document in a system for feeding and transporting documents is provided. The document has a leading edge and trailing edge. The system includes a feeder stage, including a feeder and a separator for receiving a document therebetween and gripping the document with a first grip. The system further includes a transport stage downstream of the feeder stage. The transport stage includes an accelerator driver and an accelerator idler for receiving the document therebetween and gripping the document with a second grip that is less than the first grip. When the document is simultaneously gripped by the feeder and separator and gripped by the accelerator driver and accelerator idler, the document slips at the accelerator driver until the document trailing edge exits the feeder and separator. The method comprises detecting an acceleration of the accelerator idler indicating when the document trailing edge exits the feeder and separator.
In a preferred embodiment, the method further comprises, after detecting the acceleration of the accelerator idler, performing an operation after the document trailing edge has exited the feeder and separator. Preferably, the method further comprises providing a tachometer at the accelerator idler.
In embodiments of the present invention, the tachometer may include an encoder and generate a pulse sequence. Or, the tachometer may generate an analog velocity signal.
In a preferred embodiment, the method further comprises detecting a relative acceleration of the accelerator idler with respect to the feeder indicating when a document trailing edge exits the feeder and separator. More preferably, the method further comprises providing a tachometer at the accelerator idler, and providing a feeder tachometer at the feeder.
The advantages associated with embodiments of the present invention are numerous. For example, embodiments of the present invention provide systems and methods for detecting a document trailing edge exiting a feeder. Detecting the document trailing edge exiting the feeder allows operations to be performed on a second, following, document with the feeder as soon as possible without affecting the first document. Further, detecting the document trailing edge exiting the feeder allows operations to be performed on the first, leading, document in the transport stage without the first document being affected by actions of the feeder. Systems of the present invention utilize a tachometer at the accelerator idler, while methods of the present invention comprise detecting acceleration of the accelerator idler. Many document processing products could benefit from embodiments of the present invention. For example, copiers, fax machines, sheet feeders for computer printers, automatic teller machines, and document image scanners are just a few examples of products that could benefit from embodiments of the present invention.
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the preferred embodiment when taken in connection with the accompanying drawings.